Streptomyces hydrogenans strain DEF17: a plant growth-promoting and biocontrol strain in Solanum lycopersicum

Streptomycetes have a potential role as plant growth promoters and plant protection agents. Streptomyces sp.DEF17 is a barley endophytic strain with promising plant growth promotion (PGP) and biological controlpotential. When applied to tomato seeds, DEF17 significantly increased plant height during earlydevelopmental stages.To further explore its genetic potential, a hybrid Illumina-Nanopore genome assembly was performed, allowingthe complete reconstruction of the bacterial chromosome and the identification of a 34 kb plasmid. Genomemining with AntiSMASH and PLAbase confirmed the presence of gene clusters responsible for siderophoreproduction, including desferrioxamine, suggesting a role in improving plant iron nutrition. Furthermore,functional annotation of the plasmid revealed its potential involvement in phosphate solubilization, includingphosphonate degradation pathways, and in bacterial fitness mechanisms, such as a toxin-antitoxin system(TypeIV AbiEii), which could contribute to competitive exclusion and microbial resilience in the rhizosphere.Based on these results, the siderophore activity of DEF17 was investigated in planta under two growthconditions: one with Fe(III)-supplementation and one with a standard substrate. In this regard, DEF17-treatedplants accumulated significantly higher levels of Fe, Mn, and K in leaves under Fe(III)-supplementedconditions, highlighting the effect of DEF17 on nutrient homeostasis.To further characterize DEF17, a test was performed to investigate the plant-mediated DEF17 biocontrolpotential against Fusarium oxysporum f. sp. lycopersici (FOL) through chemotropism assays. Results showedthat root exudates from DEF17-treated plants were able to repel FOL germ tubes, suggesting an active role ofDEF17 in plant modulation of fungal behavior. Preliminary metabolomic data of root exudates obtained fromtreated plants also indicated an increase in glycosylated alkaloids, such as tomatine, which may contribute tothe protective effects induced by DEF17.Overall, this study describes the potential of DEF17 to contribute to sustainable agriculture by increasing cropfitness and resilience, thus reducing in-field chemical inputs.